1. Field of the Invention
This invention relates to a device for the transmission, by radio or by cable, to a central control and recording system, of data collected from a plurality of acquisition assemblies placed at different locations.
2. Prior Art
More precisely, the invention concerns a device for the sequential transmission, by radio or by cable, to a central control and recording system, of seismic data collected from a plurality of data acquisition assemblies contained in boxes or buoys placed at a certain distance from one another. The sequentially transmitted data are signals generated by seismic sensors (geophones or hydrophones) or sensor groups interconnected in series or in parallel, distributed along a seismic profile on survey, in response to echoes on subterranean layers of seismic waves transmitted through the earth by a suitable wave generator. The sensor or sensor groups arranged along the profile are distributed in several assemblies, the sensors of each assembly being connected to a data acquisition apparatus adapted to amplify the analog seismic signals simultaneously transmitted thereto, then to digitalize and record them.
The transmission of memorized data by each acquisition apparatus may be effected by radio or through transmission cables. The central control system transmits successively transmission orders, generally in coded form, to the different acquisition apparatuses. These transmission orders, preceded by an address signal for identification of the concerned acquisition apparatus, are conveyed through conducting lines or by radio towards the different boxes or buoys distributed over the survey area. When each acquisition apparatus has detected the specific transmission order concerning it, it transfers the data memorized therein to the control and recording system through a special connection cable or it connects itself for a certain time onto one or more common transmission lines.
The radio connections are more simple to effect but the quality of the transmissions may have defects when the land where the boxes of buoys are laid down is very uneven or when obstacles impede a good transmission of the Hertzian waves (dense woods, for example). Cable connections are generally very reliable irrespective of the nature and the surface of the land, but their use requires the time consuming and costly operations of placing and displacing conducting lines, particularly in the mountainous or boggy areas.
The transmission devices known for seismic prospecting on land, generally make use of radio connections, which are more easily effected than the cable connections and cannot be easily adapted to the alternative use of the other transmission mode, when the hertzian transmissions become defective.